1. Field of the Invention
This invention relates to the use of radiant infrared burners in warm air furnaces. In particular, the invention relates to the use of such burners in a furnace having a pressure in its combustion chamber and heat exchanger that is lower than the air surrounding the furnace, with such a reduced pressure being created by an induction blower.
2. Description of the Prior Art
Warm air furnaces are used in residential and commercial applications for such purposes as heating spaces within a building. In such a furnace, air is drawn into the furnace where it is heated by contact with a heat exchanger. The air then passes to the space to be heated. The heat exchanger in turn is heated by burning fuel and the gases produced by the burning fuel. It is normal practice to produce furnaces with more than one heat exchanger, the number of heat exchangers in a given furnace being determined by heat exchanger design and by desired furnace heat output capacity.
The usual means by which a gaseous or vaporized liquid fuel is burned in a furnace is a ribbon type burner located under the heat exchanger or by what is known in the industry as an "inshot" or jet type burner whose flame is directed into the inlet of the heat exchanger. Natural convection or a blower to create a forced draft are generally used to cause the gases of combustion to flow through and out of the heat exchanger. In such a furnace, the burning process generates not only heat but low frequency sound termed "combustion roar." If the furnace is connected to a hot air ducting system, the ducting tends to amplify the sound and transmit it to spaces remote from the furnace.
The products of combustion from flame burners in the furnaces now in widespread use contain oxides of nitrogen (NO.sub.x). These oxides are vented to the atmosphere with the combustion products as flue gases. Limiting the concentration of NO.sub.x in the flue gases is desirable, as furnaces sold in certain jurisdictions must comply with very low NO.sub.x emission requirements.
The use of a radiant infrared burner in a furnace instead of the more usual flame burner has certain advantages, chief among them as pertain to this invention are that the gases of combustion produced by a radiant burner have very low concentrations of NO.sub.x and that the radiant burner burns silently, without producing combustion roar.
When a radiant burner is in operation, a mixture of a gaseous fuel and air is supplied to the interior of the burner shell. The mixture then passes through a gas-permeable material in the wall or shell of the burner and burns on the outer surface of the burner's wall or shell. To cause the mixture to pass through the gas-permeable material, the pressure within the burner must be greater than the pressure on the burner's exterior. Generally, this pressure differential is achieved by raising the internal pressure, e.g. by using a means to supply the gas/air to the burner interior at an elevated pressure (with respect to the air surrounding the furnace). With an elevated internal burner pressure, in order for the hot gases of combustion to flow from the burner to the flue, the entire gas flow path, including the heat exchanger, must be at a pressure greater than the surrounding air. If this is the case, and if there is a means for free communication of gases between the gas side and circulating air side of the heat exchanger, e.g. a hole due to damage to or deterioration of the heat exchanger shell, then combustion gas could leak from the gas side into the circulating air side of the furnace and be carried with the air to the heated spaces.
Designers in the industry have developed warm air furnaces in which a radiant burner is used, see e.g. Bratko, U.S. Pat. No. 4,314,542.